1. Field of the Invention
This invention is directed to top drive systems for use in wellbore rigs, to components of such systems, and to methods of their use.
2. Description of Related Art
The prior art discloses a variety of top drive systems which use a DC or AC motor.
U.S. Pat. Nos. 4,458,768; 5,433,279; 6,276,450; 4,813,493; 6,705,405; 4,800,968; 4,878,546; 4,872,577; 4,753,300; 6,536,520; 6,679,333 disclose various top drive systems.
The prior art discloses a Varco Drilling Systems Model TDS-9S AC Top Drive system which has an alternating current motor-powered top drive.